Trayvon Martin was on the phone up until the moments before he was killed, cellular records show, and the girl he was talking to says she could hear him when the teen asked a stranger: "Why are you following me?" First she heard, "What are you doing here?" and then a push and an altercation just before the line went dead, the attorney for the dead teen's family said. "I called him again and he didn't answer the phone," the girl said. A recording of the girl's account of Martin's last moments was among several major developments Tuesday in the investigation into the killing of the teen by a neighborhood watch volunteer in Sanford. Seminole County State Attorney Norm Wolfinger announced he would convene a grand jury next month to probe the case, which is being reviewed by the U.S. Department of Justice Civil Rights Division, the FBI and the Florida Department of Law Enforcement. With the case gaining national attention and racial tempers flaring, social media sites were exploding Tuesday with the belief that the teen's killer used a racial epithet just minutes before he shot Martin, 17. George Zimmerman, 28, an aspiring police officer who once attended a citizen police academy, called the Sanford Police Department on Feb. 26 to report a suspicious person in his gated townhouse complex. It was one of the dozens of times he had called police over the years, and one of several where he called to report the presence of a black male. After the shooting, Zimmerman told police the young man came at him from behind and attacked him, and he fired in self-defense. He was not charged, triggering national outrage and an online petition that drew more than 600,000 signatures. On the recording of his call to police, Zimmerman can be heard breathing heavily as he pursued Martin through the complex. The dispatcher told Zimmerman not to follow, saying an officer was on the way. Then, about two minutes into the call, under his breath, he used a profanity and a second word that sounded like a racial slur, but it was nearly inaudible and difficult to decipher with certainty. Like the scores of news agencies that had listened to the tape over and over since it was released Friday, Sanford police spokesman Sgt. David Morgenstern said no one at the department had noticed the muttering before Tuesday. "I listened to that tape several times, and I never heard it before," he said. "I am quite sure the grand jury will listen to it." Benjamin Crump, the attorney for the dead teen's family, said the incident was another disturbing development in a case riddled with police missteps. He was also troubled by the decision to take the case to a grand jury, which meets in private. If the roles had been reversed, "would Trayvon Martin have gotten the courtesy of a grand jury?" Crump asked. "Whatever case they put out, we won't know. They can come out ... and say, 'It wasn't us, it was the community.' " Crump, who is based in Tallahassee, flew to Miami after Martin's father combed through his son's cell phone records and discovered he was on the telephone moments before he died. The number belonged to a girl Martin had spent hours talking to that weekend, a girl he was dating. Crump recorded her statement and played it for reporters at a news conference Tuesday in Fort Lauderdale. He said he promised the girl's parents he would not reveal her name. Records show she called Martin at 7:12 p.m., and spoke to him for four minutes. Zimmerman's call to police was at 7:11. She told Crump that Martin said he was being followed. "Run!" she recalled telling him. "Trayvon said he's not running." Crump said phone records back up the girl's story, showing that the "suspicious" person who neighborhood watch thought was "up to no good" was simply a teen like any other. "This girl connects the dots," said Crump, who added he plans to turn the tape over to federal investigators, but not to Sanford police. Attorneys for Martin's family accuse the Sanford police of protecting Zimmerman because he shares their love for law enforcement. Zimmerman, who was born in Virginia and studied criminal justice at Seminole State College, is the son of a retired Virginia Supreme Court magistrate and his wife, a longtime clerk of courts, according to his application to the citizen's academy. Sanford police released a log of Zimmerman's dozens of calls to police dating back to 2004, which show a pattern of his reporting suspicious people and minor nuisances. Zimmerman was arrested in a scuffle with an undercover officer in 2005, but the charges were dropped when he entered a pretrial diversion program that allowed him to have a clean record. When he applied for the citizen's police academy, Zimmerman insisted he did not know the man he scuffled with was a cop. "I hold law enforcement officers in the highest regaurd [sic] as I hope to one day become one," he wrote in his application. "I would never have touched a police officer."